pmd: fix #1178 LexicalError while parsing Java code aborts CPD run
pmd/cpd: add skipLexicalErrors and skipDuplicateFiles to CPD's ant task
pmd: fix #1177 Incorrect StringBuffer warning when that class is not used
pmd: fix #1180 False Positive for ConsecutiveAppendsShouldReuse on different variable names
pmd: fix #1168 Designer errors when trying to copy xml to clipboard
Document that PMD requires java 1.6
Fix unit test DesignerTest so that it runs in headless mode, too.